1. Field of the Invention
This invention relates to the field of manually operable continuous controls, and in particular to a method and apparatus for digitally scaling and shifting the outputs of manual control devices such as potentiometers and the like which form the inputs to a video switcher. Levels produced by the potentiometers or the like are remapped for optimum use of the available control range in effecting a desired range of a transition. The scaling and shifting are done dynamically to adapt to the particular range of a transition, which may be dynamically affected by changes in related parameters, employing the full available range of the manual control device to correspond to the span of a desired transition making up an effect.
2. Prior Art
Manually operable control devices such as potentiometers or other mechanically variable means for producing corresponding variable electrical outputs are well known, for example as volume or level controls. Potentiometers used for such control devices typically are connected to produce a variable analog level of current, voltage, etc. as a result of the manually adjustable resistance between a movable wiper and one or both of the terminals of a resistor over which the wiper can be moved. Similar controls are also known with variable capacitance, inductance, and other parameters, however, the typical control uses a potentiometer and this form of device is discussed herein for purposes of illustration. In a typical application, the variable resistance of the potentiometer is connected to provide variable gain in an amplifier, variable biasing voltage, or otherwise arranged to produce the desired corresponding variation in the output.
Control devices have a useful control range defined by the maximum and minimum variation (e.g., in resistance) of which the control device is capable due to its physical parameters such as the series resistance between the terminals, the range of possible physical displacement of the wiper and the like. The full span of the useful range may or may not actually be needed in effecting a particular transition in the controlled parameter. When designing a control based on these manually variable devices, the engineer chooses the elements of the circuit such that the full range of all possible transitions is available to be utilized as necessary. However, a particular desired transition may not need the whole range of the control device. During a partial scale transition, the control device is moved over only a limited proportion of its full range, or if moved over the whole range typically has no effect on the controlled output for most of its range. The useful range of variation of the output occurs over a very limited range of the physical displacement of the control device.
To some extent, the various parameters in a transition effect to be controlled by a video effects switcher are related to one another. For example, if transitions in parameters affecting the size and/or position of a geometric pattern are to occur together, the operator normally must ensure that the combination of the variations in the parameters is not such as to place the geometric pattern off the scale, i.e., outside the displayable video field. Therefore, in addition to the fact that a transition in a parameter may not need the full possible range of its control, transitions in related constraining parameters may dynamically affect the extent of variation available in a particular parameter.
Controls producing an electrical level or the like are known to be useful for producing a continuously variable input to a digital processor which uses the control as a data input. This type of input is used, for example, to control the transitions accomplished in video switchers. The control potentiometer terminals are connected to fixed voltages and the wiper is connected to an analog to digital converter. The numerical output of the analog to digital converter is then sampled periodically and the digital processor effects the time-varying output which is manually changed by the operator in manipulating the control device.
The transitions controlled using a video switcher or video effects switcher may involve a partial change or a full span change over a time period of more than one video frame, from one video input signal to another. Typical switched effects are the "wipe" and the "mix," and other effects of a similar nature are also possible. A wipe is the insertion of one video signal into another, where the insertion is a predetermined shape, usually a geometric pattern. The pattern has certain variable parameters such as position, size, aspect ratio, border width, edge softness, etc. As the transition proceeds, for example under operator control using a manually variable electrical element such as a potentiometer, the pattern can be made to grow, shrink or otherwise vary. As a typical wipe proceeds, the geometric pattern grows or shrinks to reveal the new video signal on or in place of the previous video signal. A mix is a comparable time-varied transition where the full frame of video dissolves into a new frame.
It is frequently a design compromise to have the full mechanical range of displacement of a control device correspond directly with the full range of variation in the electrical output to be controlled, to cover the set of all possible parameter transitions, whereas most transitions require only a limited range within the full range possible. However, according to the invention, the full mechanical range of displacement is applied to any particular transition by remapping the full range of output of the control to cover only that portion of the available span of the output that will be used in effecting a particular desired transition, and to control the variation within this span as linearly as possible. In this manner, the user enjoys the most possible control over progress of the transition, and the full range of the manual control is always employed to control transitions through larger or smaller output ranges (according to the parameters of a particular effect) within the total available span.
"Transition magnitude" can be defined as a measure of the extent to which any parameter involved in a transition has proceeded and can be expressed, for example, as a percentage of the full available span of the controlled parameter. In known video switchers, the transition magnitude is indirectly controlled by an operator, using a transition controller which traditionally is a lever arm connected to a potentiometer, the lever mounting and the resistance span of the potentiometer defining an upper limit and a lower limit. Often the operator can also specify the number of video fields or frames which the transition should span, this being done via a digital interface. The user can specify manually the starting and ending transition magnitudes for a transition, and this is one of the reasons that a particular transition may require a limited range of the parameter within the total available span. The various parameters of the transition can be static or can change during the transition; and this is another reason that a particular transition may require only a partial span of the controlled parameter (because the instantaneous value of any non-controlled parameter can constrain the useful range of the controlled parameter). For example, a circle wipe with a border parameter of two inches, where the controlled parameter is the circle size, could require a useful size span of four units. But a circle wipe with a three inch border could require a useful size span of five units. Moreover, the set of all possible circle wipes could require a total size span of ten units. The prior art would map the full physical range of the control to ten size units for both the two and three inch border transition examples noted above, whereas the present invention would map the full physical range of the control to four size units in the two inch border transition, and five size units in the three inch border transition.
A transition is accomplished by controlling a type of video processor subsystem that has two or more video signals as inputs, one video signal as the output, and at least one control input that determines what combination of the video inputs will be present in the output. During a given video field, the controlled parameter as set by the input or inputs for a transition can be static during the transition, yielding a mix, or dynamic, yielding a wipe, matrix or the like. A transition occurs when the controlled parameter and/or control input changes over a predetermined number or sequence of fields so that the video output goes from one combination of the inputs to another combination. The control input magnitude is thereby related to the transition magnitude of each parameter which is set or changed during the transition.
During a complete transition, the user plans the effect parameters and how they will change (if at all) during the transition, then moves one or more lever arms or other similar control devices from the desired lower limits to the desired upper limits. As the transition controller responds to the control input(s), the transition magnitude of the controlled parameter is changed over time from one value to another. These desired transition magnitude endpoints, however, are a function of all the effect parameters, and for different levels and combinations of the parameters, the magnitude endpoints required to complete the transition are likewise different. For example, one might wish to have the transition magnitude of the field size or the like change only from 45% of its maximum to 55% during the transition. In that case, the operable portion of the displacement of the control device throughout the entire transition would be limited to the passage of the control device through an area very close to its midspan. Manually selectable transition magnitudes that lie outside of the required endpoints for a particular transition will have no effect on the output.
The prior art discloses the use of potentiometer controls and the like to control video switchers, for example as shown in U.S. Pat. Nos. 3,728,479 - Srinivasan; 3,989,888 - Busch et al; and, 3,758,712 - Hudson, the latter also disclosing placing switch contacts at the extremes of the span of the control device to provide further inputs to circuits controlling a transition. These disclosures show the use of control devices of the present type, but do not address the problem of ensuring that the span of the control device and the possibly limited span of transition magnitude between the desired endpoints are optimized such that the full span of the control device corresponds to the span of the change desired in the transition magnitude between the endpoints.
U.S. Pat. Nos. 4,668,989 - Mackereth and 4,713,695 - Macheboeuf disclose video switchers that attempt to digitize or optimize a change in transition magnitude over an effect. These patents also do not disclose the possibility of optimizing the range of the control device used for setting transition magnitude to the range of desired change in the transition magnitude throughout the progress of a transition or similar effect.
The fact that different effect parameters require different spans of transition magnitudes, and in particular different endpoints for the parameters changed over the transition, poses a problem for known video effects switchers. It is preferable that the user have the greatest possible ability to control the transition that is possible with a given control device (i.e., variable adjustment means). The control device should begin to affect the transition magnitude of the controlled parameter immediately when the control device for adjusting said magnitude is moved off its lower limit and the end of the span of the control device should be reached precisely when the transition magnitude reaches the desired upper limit, which may or may not be the upper limit of the full range of the controlled parameter. If the transition begins only after the control device is off its lower limit and/or end when the control device is below the upper limit, then the control device or the transition controller has "dead space" and this reduces the expression resolution available for the user attempting to control the effect. If the transition is made to occur within the span but appears abruptly, for example at the control device's lower limit, or if the transition is not completed when the control device reaches the upper limit, then the desired transition effect has not been obtained.
To attempt to encode the full mechanical span of a control device for selection of a desired change in transition magnitude of a parameter in transition, the prior art has adopted mapping of the full span of the output of the control device to the limits of transition magnitude of which the processor is capable. The lower limit of the control device can be mapped to the minimum possible magnitude of the transition magnitude. The upper limit of the control device is mapped to the maximum maximum possible transition magnitude. This technique results in dead space for most transitions because the selected maximum and minimum transition magnitudes will not always correspond to the full possible deflection. Therefore, the operation of the device is such that the control device will have no effect on the controlled parameter until off the lower limit and the operable span during which changes occur in the controlled parameter will be complete before the control device reaches its upper limit.
Some video switchers have provided a reduced level of mapping based on one particular effect parameter such as geometric pattern position. The full span of the control device is mapped to a limited span of the controlled parameter, the limited span endpoints, (e.g., desired maximum and minimum transition magnitudes) being a function of the parameter being controlled. This technique still yields controller dead space for most levels of complex effect because it does not account for all the effect's parameters, which may be interrelated. The technique of mapping the full range of a control device to the full range of the parameter, and limited mapping (full range of control to limited range of parameter) is illustrated in FIG. 3. Whether the control is based on the full range of the electrical variation possible between manual endpoints 72, 74 using the manual element 20 and potentiometer 30 or the like from the maximum possible 92 to the minimum possible 94 (solid arrows in FIG. 3) or whether the control is based on mapping a desired fractional part of the full range of electrical variation (dashed lines in FIG. 3), in either case, dead space 90 results.
The present invention takes a different approach than the known techniques in that the control device span is mapped dynamically to the magnitude of the controlled parameter for each desired effect, being recalculated at every video field. During a present video field, the parameter magnitudes (i.e., the transition magnitudes) are read and are used together with the control device setting to calculate a new mapping relationship between incremental changes in the control device setting and controlled changes in transition magnitude as required to move toward the desired endpoint of the planned transition magnitudes. The recalculation is accomplished by adjusting the output dynamically, by an amount which will ensure that the span of the control device will be used up at the same time that the transition magnitude reaches the desired endpoint. The result of this technique is illustrated in FIG. 2, wherein regardless of the endpoints or the span of a particular transition, the full manual range of the control device is caused to correspond to the required range of the effect. The process involves scaling and shifting the detected difference in the level set by the control device by the ratio of the change in transition magnitude to the distance yet to go toward the endpoint. The endpoint can be constrained, also dynamically, where changes in related parameters are such as to move the previous endpoint off the scale. The invention results in a transition controller with no dead space, and without any abrupt starting or stopping of the transition at a limited area of the control device span. The invention achieves excellent control accuracy and linearity but does not require expensive additional hardware because the remapping is done by calculations conducted by the video effects processor.